Liquefied petroleum gas ("LPG") fuel supply systems are known, for example as shown in Applicant's U.S. Pat. Nos. 5,291,869; 5,325,838; and 5,423,303. Such systems typically include a number of specialized fuel injectors which receive fuel from a high pressure tank. A fuel rail connected in-line with a series of injectors is often employed to deliver supply fuel to the injectors. In many systems, uninjected fuel is returned to the fuel tank. This is generally done to keep the supply fuel as cool as possible, particularly where it is intended to inject LPG in liquid rather than gaseous form.
One approach to injecting LPG without permitting it to vaporize is to pump high volumes of supply and return fuel. In this way, the supply fuel spends very little time near the heated engine compartment where it can vaporize. Another approach is to employ a refrigeration cycle as described in the Applicant's patents identified above. The evaporation of return fuel is used to cool supply fuel, thereby maintaining it in liquid form.
A problem with returning vaporized LPG to the fuel tank is that it can increase tank pressure substantially above the vapor pressure of the liquid in the tank. If the vapor does not condense before the pressure limit of the tank is exceeded, the pressure relief valve will release LPG vapor to the atmosphere. This is both unsafe and environmentally undesirable.
What has been needed is a way to cool return fuel in ILPG systems so as to reduce the high fuel tank pressures which can occur.